Open Extract pages from the Home screen (or use its own page link).
Tap Choose file and select your PDF from the phone or computer.
Under Which pages? choose Type page numbers (then write them like 1-3,5), Odd pages (1,3,5…) or Even pages (2,4,6…).
Tap the big purple Start button and wait a few seconds.
When you see Done!, tap Download. The new file is saved on your phone or computer.